Hitting a baseball is one of the most complex body actions in sport. It requires total body synchronicity, precise eye-hand coordination, balance, timing, rhythm, and strength. A proper understanding of the different parts of the swing will help you teach your players hitting, help correct their mistakes and help you develop successful hitters.
Tip: When practicing, especially at the younger levels, try and incorporate some form of coordination exercises at every practice. The better your kids can become at controlling their bodies, the better baseball players they will be. Examples: skipping rope, one leg balancing, simple jumps, target practice, switch hitting, juggling, one handed catches, etc. One last note, as kids get older, pay special attention to their flexibility and range of motion in their joints.